Ch.21 Populations & Communities Section 3: Interactions Among Living Things

Section 3 Adapting to the Environment – Natural Selection: a characteristic that makes an individual better suited to its environment may eventually become common in that species through this process – Adaptations: the behaviors and physical characteristics that allow organisms to live successfully in their environments – Niche: the role of an organism in its habitat, or how it makes its living Every organism has a variety of adaptations that are suited to its specific living conditions

Section 3 Competition – That are three major types of interactions among organisms: competition, predation, and symbiosis competition

Section 3 Predation: an interaction in which one organism kills another for food – Predator: the organism that does the killing – Prey: the organism that is killed – The Effect of Predation on Population Size – Predator Adaptations – Prey Adaptations

Section 3 Symbiosis: is a close relationship between two species that benefits at least one of the species – The three types of symbiotic relationships are mutualism, commensalism, and parasitism

Section 3 Symbiosis – Mutualism: a relationship in which both species benefit

Section 3 Symbiosis – Commensalism: a relationship in which one species benefits and the other species is neither helped nor harmed

Section 3 Symbiosis – Parasitism: involves one organism living on or inside another organism & harming it – Parasite: the organism that benefits – Host: the organism it lives on